Edward H. Bennett described the intra-articular
fracture-dislocation of the first metacarpal base in 1882. (1) He noted
the thumb's functional importance, stating "no injury of it is
to be lightly regarded." (1) Injury to the first metacarpal
frequently occurs, accounting for 25% of all metacarpal fractures, 80%
of which involve the base, the Bennett fracture being most common. (2)
The goals of treatment are to maintain motion and the biomechanics of
the trapeziometacarpal joint by restoring the joint's anatomic
congruity and articular surface and correcting carpometacarpal
subluxation or dislocation. (3) Investigators postulate that accurate
reduction of the CMC joint helps prevent the development of arthritis in
an articulation already at increased risk. (4,5) For non-displaced
fractures, treatment in a thumb-spica cast can be tried. (1,6,7) For
displaced fractures, closed reduction and percutaneous pinning (CRPP) is
preferred for small fragments with minimal articular step-off. (8-10)
Open reduction and internal fixation (ORIF) is often indicated for large
fracture fragments with displacement greater than 2 mm that are
irreducible with closed methods. (2-4,5,11,12) Recently, investigators
have described arthroscopic osteosynthesis of displaced Bennett
fractures. (13,14) More than 20 methods of treatment have been
described, reflecting the lack of clear consensus on optimal treatment.
(15) The purpose of this article is to review the relevant anatomy,
biomechanics, clinical evaluation, classification, treatment options,
and controversies that exist for treatment of the Bennett fracture. We
also present our preferred treatment methods given the available
literature.

Anatomy

The trapeziometacarpal joint is unique in that it is a double
"saddle" joint. (3,16) The articular surfaces of the thumb
metacarpal base and trapezium resemble reciprocally interlocking
saddles, allowing for flexion-extension, abduction-adduction, and
rotation. (3,16) Motion is coupled; pronation is combined with flexion
and hyperextension with supination of the CMC joint. Metacarpal muscular
insertions include the abductor pollicis longus (APL) at the proximal
base, the adductor pollicis distal and ulnar, and the thenar muscles
volarly. Ligamentous CMC joint stability is provided by the
anterior-volar-oblique (beak) ligament, the posterior oblique, dorsal
radial, and anterior and posterior intermetacarpal ligaments. (17)
Nearly half the stability of the joint is conferred by its biconcave
nature. The beak ligament is the most significant capsular reinforcement
and resists dorsal and radial subluxation during a key pinch by
stabilizing the dorsal-radial capsule. In addition, it provides 40% of
the resistance to pronation. (17) The beak ligament originates from the
trapezium and inserts on the volar beak of the thumb metacarpal base.
Resistance to supination is provided by the intermetacarpal ligament
between the first and second metacarpals.

Biomechanics

The mechanism of injury is an axial load on the partially flexed
thumb metacarpal leading to an intra-articular avulsion fracture of the
volar ulnar metacarpal base from the remaining thumb metacarpal. The
pull of the APL, the thumb extensors, and the adductor pollicis
displaces the thumb metacarpal radially, dorsally, and proximally (Fig.
1). The volar ulnar corner of the metacarpal base remains in place,
tethered by the strong volar oblique ligament.

Cooney and coworkers found that with a key pinch, the CMC joint
sees compressive forces up to 12 times higher than the force being
produced. (18) High daily forces coupled with the relatively increased
mobility of the trapeziometacarpal joint places increased stress on the
articulation. This helps explain the CMC joints propensity for arthritis
and the potential importance of surgical intervention in Bennett
fractures.

Patient Evaluation

The majority of Bennett fractures occur in men, with more than half
occurring in the dominant hand. (1,2) The history and physical exam is
an important part of the diagnostic process. Patients will often report
a fall onto the affected hand or direct axial load. They will report
immediate pain and swelling at the base of the first metacarpal. On
examination, they will have tenderness at the base of the CMC joint.
Crepitus with attempted motion and decreased range of motion will be
present. A palpable "shelf' deformity at the base of the
metacarpal can result from displacement of the metacarpal shaft
dorsally.

Imaging

Radiographs are essential for diagnosis. All patients should
receive PA, lateral, and oblique images of the thumb. A true lateral
view as described by Billing and Gedda is necessary to correctly view
the articulation of the base of the first metacarpal at the first CMC
joint. (19) This view is obtained by pronating the hand 20[degrees] and
then angling the beam 15[degrees] to 20[degrees] distally. In addition,
traction radiographs have been described to help assess the effect of
ligomentotaxis on the reduction. (3) A computed tomography scan can be
considered in comminuted fractures.

Classification

In 1952, Gedda published a series of Bennet fractures that had been
treated non-operatively and proposed a classification system consisting
of three types. (20) Type 1 is defined as a fracture with a large single
ulnar fragment and subluxation of the metacarpal base. Type 2 is defined
as an impaction fracture without subluxation of the thumb metacarpal.
Type 3 represents a small ulnar avulsion fracture fragment in
association with metacarpal dislocation (Table 1). (20)

Non-Operative Treatment

Historically, the majority of these injuries were treated with
closed reduction and casting for 4 to 6 weeks. (1,6,7,21) Reduction is
obtained by applying axial traction, palmar abduction, and pronation to
the thumb metacarpal while providing pressure over the dorsal-radial
metacarpal base (Fig. 2). The hand is then placed into plaster
immobilization in a thumb-spica splint in an attempt to maintain
reduction. During the 1960s, long-term studies analyzing non-operative
management showed frequent loss of reduction with resulting
posttraumatic arthritis, shifting management toward operative fixation.
(6,7) Gedda and Moberg reported a series of 54 patients, 49 of which
were asymptomatic after non-operative treatment. (2) However, they
became early proponents of open fixation due to evidence of loss of
reduction and radiographic findings of arthrosis in 41 of these
patients. (2) Despite the radiographic arthrosis seen on imaging and
clinical findings of loss of motion in abduction and extension, patient
satisfaction remained high in some series. (6,21) However, in 1990,
Livesey reported a series of 17 Bennett fractures treated with casting
with 26-year follow-up. (22) Six patients had severe pain, 12 had
persistent gross deformity, and 13 had persistent subluxation of the CMC
joint. All patients had loss of thumb abduction and extension and a
decrease in grip strength. They concluded operative means should be
employed. Non-operative treatment is now mainly reserved for
non-displaced Bennett fractures. (22)

Operative Treatment

Percutaneous pinning is one operative option to maintain articular
reduction and correction of metacarpal subluxation and has the advantage
of avoiding associated complications of open surgery, including tendon
adhesions and bone necrosis. In 1950, Wagner reported 38 cases treated
with CRPP across the trapeziometacarpal joint and found "uniformly
good results." (10) Van Nierk recommended transmetacarpal pinning
to spare the already threatened CMC joint articular cartilage. (9) He
found no limitations in daily activities, work, or sporting hobbies. In
2012 Greeven reported on seven Bennett fractures with 2-year follow-up
treated with transmetacarpal pinning. (8) Surgical time ranged from 6 to
20 minutes, no complications were reported, and none of the patients
experienced "any functional limitations." (8)

While series have shown acceptable results with CRPP, the ability
to obtain an anatomic reduction using closed methods has been
questioned. (23,24) Capo and colleagues simulated Bennett fractures in
eight cadaveric specimens and then compared the articular reduction
using fluoroscopy and direct visualization of the joint after CRPP. (23)
Fractures were created through an open incision, skin closed, and CRPP
performed. They found a significant difference in articular step-off
(< 0.001) and displacement (< 0.01) measured using fluoroscopy
versus subsequent open examination. (23) However, Greeven and associates
could not replicate these findings and did not find differences in
displacement or fracture step-off between fluoroscopy, plain
radiographs, and direct visualization. (24)

In a cadaveric biomechanical study, Cullen and coworkers measured
the contact area and pressures of the first CMC joint after artificial
Bennett fracture, with fragments fixed with a 2 mm joint step-off. (25)
They found an overall increase in CMC joint contact area; however, there
was no pathological pressure increases. In fact, there was a decrease in
palmar contact forces with a slight increase in dorsal forces. They
concluded that a Bennett fracture with a 2 mm step-off should not
precipitate a post-traumatic arthrosis and may actually be protective,
and therefore, CRPP to restore articular surface with up to 2 mm of
step-off should be the first treatment of choice. (25)

Classically, ORIF has been recommended when the fracture fragment
is greater than 15% to 25% of the articular surface and when the
articular surface cannot be reduced to less than 2 mm of displacement
with closed methods. (2,4,11,26,27) If open reduction is going to be
performed, a Wagner incision is generally utilized. (10) This incision
follows the thenar eminence in a gentle curve toward its palmar aspect.
In general, studies evaluating ORIF have produced favorable results.
(2,4,11,26,27) ORIF allows for anatomic reduction, which prevents the
development of radiographic arthritis associated with malreduction. In
2012, Leclere and colleagues reported a series of 24 patients undergoing
ORIF with an average of 83 month follow-up. (28) Reduction with less
than 1 mm step or gap was obtained in all patients and was maintained in
96% of cases. Pinch and grip strength measured at 4 months was 92% and
89% of the unaffected side, respectively, and did not increase
significantly at long-term follow-up. The average visual analog scale
pain score was 1.4 (scale range: 0 to 10), and all but one patient could
"practice daily life and sports activity at the same level as
before surgery." (28)

It is unclear if the radiographic changes seen in Bennett fractures
are clinically significant. Leclere and colleagues could not find a
correlation between "accuracy of the fracture reduction considering
a gap and step less than 2 mm and development of arthritis." (28)
Kjaer-Peterson and associates and Thurston and coworkers reported
medium- to long-term follow-up (average 7.3 and 7.6 years, respectively)
showing superior radiographic results could be obtained when there was
less than 1 mm of displacement. (45) Only Kjaer-Peterson and associates
could correlate this finding clinically. (4)

Studies comparing ORIF and CRPP are limited. In 1994, Timmenga and
colleagues compared 18 patients (7 CRPP, 11 ORIF) with mean follow-up of
10.7 years. (29) There was no correlation between the method of
treatment and the development of arthritis, but there was a significant
correlation between the degree of reduction and the development of
arthritic changes. However, there was no correlation between the extent
of radiographic arthritis and symptoms as five of seven patients with
exact reduction still proceeded to develop arthritis. (29) In 1990,
Kjaer-Peterson and associates reported on 41 patients treated with
either casting (9), CRPP (6) or ORIF (26). (4) Excellent reduction (<
1 mm step-off) was obtained in 5, 4, and 18 patients, respectively. At a
mean follow-up of 7.3 years, 31 patients were reviewed. Fifteen of 18
patients with excellent reduction were asymptomatic, as opposed to 6 of
the 13 with residual displacement. As stated previously, this correlated
with radiographic results. The investigators advocated "exact
reduction, if necessary by open reduction." (4) Lutz and coworkers
in 2003 compared 15 patients treated with ORIF and 17 with CRPP with
mean follow-up of 7 years, excluding patients with greater than 1 mm of
step-off. (30) They found no difference in clinical or radiographic
arthritic outcomes between treatments but did find a significantly
higher incidence of adduction deformity with pinning. The investigators
prefer CRPP for Bennett fractures with a large fragment, with ORIF
"reserved for irreducible fractures and cases when a Kirschner wire
cannot be placed in the uninjured bone at the base of the thumb
metacarpal." (30)

Recently, arthroscopic reduction and internal fixation of Bennett
fractures was described. (13,14) Theoretical advantages to ORIF include
decreased damage to surrounding soft tissues and vascular supply while
direct visualization of the joint surface provides an advantage over
CRPP. Zemirline reported a series of seven patients treated
arthroscopically, concluding this technique facilitates "joint
reduction but does not guarantee stability of fixation." (14) There
is no data supporting the utilization of arthroscopic fixation in favor
of CRPP and ORIF at this time.

Discussion

Bennett fractures have been treated since 1882, yet optimal
management is still unknown. Definitive treatment recommendations are
difficult to make because of limited follow-up and lack of prospective
randomized studies. For the majority of fractures, operative fixation to
restore articular incongruity and correct joint subluxation is
recommended. However, this is based on data consisting of small
retrospective case series or cohort studies and is conflicting on the
preferred type of operative treatment. The literature is unclear
regarding what is considered an acceptable articular reduction and
whether a small articular step-off (< 2 mm) will have long-term
clinical effects, even with evidence of radiographic arthrosis. It is
yet to be determined if the benefits of ORIF outweigh the risks when
compared to CRPP in order to prevent potentially clinically
insignificant radiographic changes of the CMC joint.

Randomized prospective trials with long-term follow-up comparing
CRPP versus ORIF in patients with Bennett fractures would help us
understand the difference between the clinical outcomes of the two
treatments. This would help assess the relationship between residual
articular step-off and the development of first CMC joint radiographic
arthrosis, and whether such arthrosis has any clinical significance. In
addition, further studies of arthroscopic fixation are needed to
determine its indications and effectiveness.

Author's Preferred Treatment

For patients with non-displaced Bennett fracture, we recommend a
trial of closed reduction by applying axial traction, palmar abduction,
and pronation to the thumb metacarpal while providing pressure over the
metacarpal base followed by immobilization in a thumb-spica splint or
cast for 4 to 6 weeks. These patients require close radiographic
follow-up to ensure adequate reduction. Patients with displaced Bennett
fractures with CMC subluxation require operative intervention. We
recommend CRPP with 0.045 Kirschner wires placed from the metacarpal
into the trapezium after performing the above reduction maneuver and
confirming reduction on fluoroscopy. If CRPP achieves correction of the
CMC subluxation, even in the setting of incomplete articular reduction,
we would not convert to ORIF. If CRPP cannot achieve an intraoperative
reduction with less than 2 mm of articular step off, we would proceed to
ORIF utilizing a Wagner incision to expose the metacarpal base. If a
large fragment is present, then two 2.0 mm screws can be used for
interfragmentary fixation along with Kirschner wires, as described
previously, for increased stability (Fig. 3). If the fragment is small,
multiple Kirschner wires can be used to maintain reduction. After CRPP
and ORIF, the patient should be placed into a thumb-spica cast for 4 to
6 weeks. Patients are advised to expect some stiffness and loss of
motion in abduction and extension as well as loss of grip strength and
post-traumatic arthritis.

Conclusion

The optimal treatment of Bennett fractures continues to be
controversial among orthopaedic surgeons. The lack of randomized,
long-term studies with large patient numbers means there are no
definitive treatment algorithms available. While most physicians would
agree that displaced fractures require operative intervention, the
treatment option of choice continues to be debated. Regardless of the
ultimate treatment method decided on, the treating physician must make
sure that the fracture is well reduced without residual subluxation
prior to leaving the operating room.

Disclosure Statement

None of the authors have a financial or proprietary interest in the
subject matter or materials discussed, including, but not limited to,
employment, consultancies, stock ownership, honoraria, and paid expert
testimony.

Caption: Figure 1 Bennett fracture subluxation of the first
carpometacarpal joint. Deforming forces include adduction and supination
of the first metacarpal by the adductor pollicis. The abductor pollicis
longus displaces the first metacarpal proximally relative to the
residual ulnar fragment, which is held in place by the palmar oblique
ligament.

Caption: Figure 2 Closed reduction of Bennett fractures is obtained
by applying axial traction, palmar abduction, and pronation to the thumb
metacarpal while providing pressure over the dorsal-radial metacarpal
base.

Caption: Figure 3 A, Bennett fracture with large ulnar fragment. B,
Same fracture status after open reduction and internal fixation with two
2.0 mm interfragmentary screws, augmented with Kirschner wire fixation.
C, 4 week's after surgery with removal of the Kirschner wire.